JP4039546B2 - Non-contact on-line hot wall thickness measuring method and apparatus for pipes - Google Patents

Abstract

Laser-ultrasound technique is used to scan a segment of the pipe wall in circumference direction, during or after the rolling process. Mathematical analysis and symmetry observations are used in a computer to reconstruct the wall of the pipe cross-section. By using several measuring heads that are swivelable in the circumference direction, each head covers a different allocated section of the pipe wall. An Independent claim is included for an apparatus for contactless hot-wall thickness measurement.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-contact online hot wall thickness measuring method and apparatus for detecting undesired inner wall structures such as hexagonal holes in hot rolled tubes, particularly stretch reduced tubes.
[0002]
[Prior art]
When producing seamless and welded steel pipes, so-called stretch reducers are often used to produce a very large number of finished pipes with different diameters and wall thicknesses from a small number of pre-determined crude products. The advantage of this method, which does not require an inner tool, is that the wall thickness and diameter can be changed quickly and at low cost.
[0003]
The deformation of the raw tube is performed by a rolling stand arranged in a large number. In this case, a change in the number of revolutions of the individual stands causes a predetermined tensile force between the stands, thereby appropriately adjusting the wall thickness of the finished tube. Deformation in the stretch reducer rolling line is now generally performed on a 3 roll stand or a 4 roll stand. The hole type of the roll stand is not formed in a round shape, and three or four surfaces are formed in an elliptical shape. This shape of the hole type is basically inevitable, and only the last stand of the stand row to be used is generally formed in a circular shape. This is because the tube to be finish-rolled is sufficiently round.
[0004]
Due to the elliptical sizing, the wall thickness of the cross-section of the stretch-reduced tube is often very uneven. This wall thickness non-uniformity has various shapes. For example, in the case of a three-roll stand, it is a hexagon and is called a polygonal hole. In the case of a 4-roll stand, it is an octagon. Like all other wall thickness deviations, the formation of a polygonal hole degrades quality.
[0005]
The formation of polygonal holes depends in particular on the wall thickness, in other words the wall thickness relative to the tube diameter, so different sizing of the roll, i.e. different ellipticity of the roll sizing, is required to generate a large wall thickness range. is there. However, since it takes a great deal of cost to prepare a rolling stand, two hole molds are generally used. That is, a hole type having a round hole with a small ellipticity for a thick-walled tube and a hole type having an elliptical hole with a large ellipticity for a thin-walled tube are used. Furthermore, it has been attempted to reduce the formation of the generated hexagonal hole by optimally adjusting the average tensile stress or tensile force of the rolled material during deformation. This attempt has shown that the polygonal dimensions change depending on the tension. This optimization of tensile force has been a very laborious task, but pipes that do not have polygonal holes are not always obtained. This is because an actual change of inevitable influence factors occurs. That is, the formation of polygonal holes must be accepted because of the deformation conditions that actually change, and enormous costs are required to perform optimization prior to manufacturing.
[0006]
Seamless steel pipes are generally produced in three deformation stages: drilling on a tilt mill, stretching on an Assel mill, Conti mill or other rolling mill and finish rolling on a stretch reducer mill. All three deformation stages produce characteristic and undesirable deviations from the nominal dimensions in the tube wall. This deviation is overlaid by each subsequent deformation stage and reappears on the stretch-reduced tube wall in this overlaid form. For example, in a two-roll inclined rolling mill, two wall thick portions extending spirally around the pipe are generated. This wall thick part appears in the cross section of the tube as an eccentric part extending in the circumferential direction. When the second deformation stage is performed in the Assel mill, a spiral thick portion extending around the tube is generated. This wall extends in the same direction, but around the tube at a different pitch, or has the opposite direction of rotation and intersects with the spiral of the stretch reducer mill.
[0007]
On the other hand, in the case of a pipe that has been roughly rolled by a continuous line and stretch-reduced, in addition to the internal hole of the SRW (inclined rolling mill, rotary piercing rolling mill) and the eccentric body extending in the circumferential direction of the inclined rolling, Is formed. This square is visible at that phase position at the SRW exit . Therefore, in order to deal with this internal defect, its precondition is given.
[0008]
The undesirable wall structure problem that occurs in the case of tubes is solved when internal defects are corrected by the control circuitry during the manufacturing process. For example, this can be solved by changing the tension parameter (changing a series of rotation speeds). As is well known, there is a unique relationship between tensile force distribution parameters and internal hole formation, so internal hole formation can be automatically reduced without affecting the wall thickness of the tube. Is possible. However, for example, when the tube exits the rolling mill with its center kept constant, the wall thickness of the hot-rolled tube is measured in a non-contact manner immediately after rolling, so that the extension of the internal hole and the defects superimposed on it are known. It is a prerequisite. However, this presupposes an economical measuring method and a low-cost measuring device. This measuring method or measuring device provides important information about the polygonal holes that occur during stretch reduction, as well as the measurement of wall thickness conditions over the length of the tube or over the passage time.
[0009]
[Problems to be solved by the invention]
Starting from the aforementioned problems of the state of the art, the object of the present invention is to minimize unwanted wall structures, such as polygonal holes, eccentric bodies or squares, in order to take early measures to improve quality. It is to provide a non-contact on-line hot wall thickness measuring method and apparatus that can be detected at the measurement technical cost of the above.
[0010]
[Means for Solving the Problems]
This object is achieved in the method according to the invention by hot rolling using a measuring device comprising up to four laser-ultrasound-measuring heads distributed around the tube to be measured. The portion of the inner wall structure of the pipe that has been formed is scanned by rocking the measuring head in the circumferential direction of the pipe during the rolling process or immediately after the rolling process. Reconfiguring by computer as an undesired inner wall structure of the tube using symmetry, each measuring head scanning a different inner polygonal part as an undesired inner wall structure of the tube, Solved by scanning at least one of these measuring heads by rocking in the circumferential direction of the tube over an angular portion determined depending on the inner polygonal shape of the undesired inner wall structure of the tube It is.
Furthermore, the above-mentioned problem is a device according to the invention, comprising a measuring device consisting of a maximum of four compact laser-ultrasound-measuring heads distributed around the tube. An optical element is housed in the head together with the excitation and irradiation laser to collect the carrier light including the ultrasonic signal reflected from the surface of the tube, and the symmetry of the polygonal shape inside the wall of the cross section of the tube Is connected to a measuring device, including an electronic control and evaluation device for reconfiguring the tube as an undesired inner wall structure, wherein the measuring head is connected to the tube by a rocking device. This is solved by being configured to be able to swing in the circumferential direction over a desired inner wall structure.
[0011]
The principle of ultrasonic-passage time measurement is applied by the laser-ultrasonic-wall thickness measurement method. Since the speed of sound is known, the wall thickness to be examined can be determined from the time that the ultrasonic pulse passes (twice) through the tube wall. When measuring the thickness of a hot wall having a temperature on the order of 1000 ° C., the measurement head and the measurement substance must be connected in a non-contact manner by means of ultrasonic waves, and therefore an optical method is used. . In the case of this method, the measuring head itself can be at a thermally safe distance from the measuring substance. High energy light pulses in the infrared range, generated by a flash lamp laser directed towards the measuring substance, are absorbed at the tube surface. This results in the attenuation of a very thin surface layer. This attenuated pulse produces an ultrasonic pulse based on the maintenance of the pulse in the tube. This ultrasonic pulse enters the tube wall perpendicular to the tube surface. The ultrasonic pulse generated in this manner is reflected on the inner surface of the tube, returns to the outer surface, and is newly reflected, so that an ultrasonic echo train having a decreasing amplitude is generated in the measurement substance. The reflected ultrasonic pulses generate subminiature range vibrations on the tube outer surface. This vibration can be detected in a non-contact manner by a continuous laser beam using the Doppler effect. A low frequency US signal compared to the optical frequency causes a frequency modulation of the light reflected at the material surface.
[0012]
The reflected cone-shaped light, which is the “carrier” of the ultrasonic signal, is supplied to an optical demodulator and a confocal Fabry-Perot interferometer through a highly luminous condenser lens and a light wave conductor. This output signal already contains an ultrasonic echo train. Further signal evaluation of amplification, filtering and ultrasonic echo trains is performed by a “conventional” ultrasonic electronic evaluation device. The output signal of this ultrasonic electronic evaluation apparatus is a wall thickness value. This wall thickness value is further processed by a computer belonging to the apparatus.
[0013]
By scanning the segment of the tube wall according to the invention, undesired structures in the tube cross-section that degrade the quality can be detected with minimal measurement technical costs. For example, when using a Ruppe welded with an SRW line, the polygonal hole (hexagon or octagon) that fixes the position of the phase is already a single channel by point laser-ultrasound-wall thickness measurement. That is, it is measured by one measuring head and recognized by it. Means for quality improvement can be taken by the mill operator as soon as possible.
[0014]
In an embodiment of the invention, at most four measuring heads are distributed around the tube and at least one of these measuring heads is determined depending on the expected order of the undesired internal structure. It is swung across the segment in the circumferential direction of the tube. When the structure is overlapped and extends in the circumferential direction (for example, stretch reduction of Assel Rupe), only three measuring heads to scan (three points define a circle, at least one of which can swing in the circumferential direction) Using the symmetry property, the same information as the tube structure information obtained with seven or more fixed measuring heads can be obtained. In the case of oscillating measuring heads or in the case of a fixed scanning measuring head or a combination of oscillating scanning measuring heads, the tube cross section is reproduced by mathematical analysis (eg Fourier analysis), superposition and symmetry considerations. Is done.
[0015]
According to another characteristic of the invention, the oscillation cycle of the measuring head is preferably determined depending on the rolling speed. For example, a relatively long oscillation cycle with a period of approximately 10 seconds is sufficient to make the formation of polygons visible during rolling times on the order of 30 seconds.
[0016]
In order to be able to detect the deviation of the tube wall cross section, the measuring head is connected to an electronic evaluation device. The electronic evaluation device is preferably arranged protected from the measuring device in the electronic switching device or in the measurement cabin. An operator PC near the stretch reducer rolling mill belongs to the measuring device.
[0017]
A conventional electronic evaluation apparatus performs amplification, filtering, and signal evaluation of an ultrasonic echo train. The output signal of this ultrasonic echo train is a wall thickness value, which is further processed by a computer.
[0018]
In order to measure the raw tube produced by the inclined rolling process and the stretch-reduced tube, three measuring heads are evenly distributed around the tube and can be swung together by about 70 °. As described at the beginning, in the case of this pipe, in addition to a hexagon or a polygon, an eccentric portion that generally extends in the circumferential direction is generated behind the stretch reducer mill. In the case of three measuring heads arranged at 120 ° and swinging together, this eccentric part can be freely determined for each angular position regardless of the polygon in which the internal eccentric part is superimposed. Thus, all three measuring heads can be affected.
[0019]
Instead, according to another feature of the present invention, the four measuring heads L1-L4 are evenly distributed around the pipe in order to measure the stretch-reduced pipe, in which the blank is produced by a tilt rolling process. Distributed and at least one of these measuring heads can swing about 70 °. In this case, the at least one measuring head detects the extension of the eccentric wall.
[0020]
In the measuring method according to the invention, three or four measuring heads are distributed on the outer circumference of the pipe in order to measure a tube that has been roughly rolled and stretch reduced in a continuous rolling line, and at least one of these measuring heads. The piece can swing about 90 °. In the case of continuous rolling, the formation of the quadrilateral overlaps with the hexagonal shape of the stretch reducer rolling mill and the circumferential eccentric portion of the tilt rolling mill. In this case, the square phase position at the exit of the stretch reducer rolling mill can be recognized again. With up to four measuring heads, at least one of which can be swung, all wall anomalies occurring there can be detected and finally eliminated.
[0021]
The measuring method and measuring device according to the present invention can also be applied to the case of an Elhard push bench device. In this case, the number of channels and the swing angle of the measuring head must be adapted to the actual structure.
[0022]
The effect of the present invention is to use a measuring head that can be rocked at least individually and operated by a laser-ultrasonic method. By detecting, it is possible to detect and use more quality features than a conventional stationary multi-channel device with a relatively small number of measuring heads and using prior knowledge about the rolling process. This will result in significant cost savings and an economical process.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in detail based on various schematic views.
[0024]
FIG. 1 shows an apparatus with only one measuring head L. This measuring head is swung to a position L ′ by an angle ψ around a rotation point X at the center of the tube 2. The hexagon shows the thinnest wall S _min and the thickest wall S _max . The shape of the polygon is regular. This is because the center of the outer circle and the center of the polygon are at the intersection X of both center lines. FIG. 1 shows a hexagon and a swing angle of the scanner L of 70 °. For other hexagonal, as shown in FIG. 5, in order to be able to reproduce the cross-section of the entire tube is sufficient swing angle of 30 ° from S _min to S _max. Therefore, an angle of 70 ° produces twice the safety. This is because two mirror-symmetric sections of the tube can be detected and compared, and the validity of the measurement result can be easily checked.
[0025]
The original measuring device for measuring hot wall thickness online and non-contactingly consists of at least one compact laser-ultrasound-measuring head L1 adjustable to the tube size to be measured. In this measuring head, an excitation / irradiation laser 8 is housed together with an optical element 9 (see FIG. 4) to collect carrier light including an ultrasonic signal reflected from the surface of the tube 3 and is not shown. The rocking device can be swung in the circumferential direction across the segment of the tube 3. In so doing, it basically does not matter what kind of oscillating device, only the ability to detect a defined segment around the tube.
[0026]
FIG. 2 shows a cross section of a tube 3 having an inner hexagon or hexagonal hole 4. The center Z of the hexagonal hole is separated from the center Y of the outer circle 5 by a distance E. Since this eccentricity of the tube is formed by a circumferentially extending spiral, the spacing E extends around the center Y in the longitudinal direction of the tube, so that the thinnest and the thickest portions _Smin and _{Smax of the} tube 3 (FIG. 1). ) Also extends around the center Y. The three measuring heads L1 to L3 are distributed at an equal distance from the center Y of the tube at an angle of 120 ° around the tube in the basic position. All three measuring heads reciprocate in the same direction and swing around the tube by an angle ψ, and swing from measuring heads L1 to L1 ′, from L2 to L2 ′, and from L3 to L3 ′. The measuring head L1 is shown, for example, in the horizontal direction, but at its basic position, it can be adjusted so that its swing angle is symmetrical with respect to the inner polygon. For example, in the case of a rocking angle ψ of 70 °, it is inclined 5 ° obliquely downward with respect to the horizontal plane.
[0027]
The oscillating measuring heads L1 to L3 have the advantage that their basic angular position or oscillating angle ψ can change during rolling. As shown in another example of FIG. 3, for example, the measuring heads L1 to L3 can be changed so that their swing angles ψ partially overlap at their basic positions starting from the positioning of FIG. . FIG. 3 shows three measuring heads L1 to L3. The measuring heads are offset from each other by 70 ° at the basic position. When the scanner swings by ψ1 = ψ2 = ψ3 = 70 °, the angle ψ2 is scanned twice, and the measurement points are scanned so as to have a predetermined deviation from each other. That is, the amount of measurement points per unit area can be doubled or tripled. That is, during operation, the controlling person differs from the normal position where the angular position of the scanner is measured with a normal resolution, and the measurement raster is made dense with a predetermined length of the tube, and the actual tube portion is enlarged and displayed. Adjustment (loupe function) can be considered.
[0028]
Next, based on the enlarged view of FIG. 4, the principle of the present invention will be described using a single-channel measuring head as an example.
[0029]
The measuring device comprises a measuring head L1 adjustable to the diameter of the tube 3 to be measured. To this measuring head, a supply element 5 (compressed air, cooling water), an electronic control / evaluation device 6 and an operator PC on the control stand 7 of the SRW belong. The measuring head L1, the electronic control / evaluation device 6 and the control stand 7 provided at the site can be provided far apart. Basically, the wall thickness measuring device is designed to withstand severe ambient conditions in a hot rolling mill.
[0030]
The measuring head L1 with a special casing with a water-cooled front face and a glass heat-resistant window substantially comprises the elements described below (not shown because they are known). That is, a flash lamp pumping Nd: YAG pulse laser, a focusing lens head, a detection branching unit having a cw laser including a controller, an infrared filter, a magnifying optical device having a direction changing mirror and a direction changing prism, and a tube surface An ultrasonic excitation branching unit provided with a highly transmissive imaging lens for condensing scattered US modulated light.
[0031]
And a sensor device (not shown) for recognizing the pipe inlet for generating the start / stop signal,
A measuring head adjusting mechanism including a swinging device, a radius adjusting means, and a means for adjusting the height (interval h) to the roll center;
Manual or fully automatic dimensioning device (distance d) when changing the tube diameter;
Measuring head moving device (powered fine movement device), with mechanical stopper for service and measuring position,
In order to be able to change the measurement trajectory between the minimum and maximum walls behind the stretch reducer mill when forming a thick polygon, i.e. the measurement head can be swung Therefore, i, d, R, absolute value transmitter and end position monitoring device equipped with an angle adjusting device (angle ψ) capable of adjusting only an angle segment of about 30 °, an automatic automatic angle adjusting device equipped with a driving device Belongs to the range of the measuring head L (see FIG. 5).
[Brief description of the drawings]
1 shows a device according to the invention with one measuring head. FIG.
FIG. 2 shows a cross section of a tube having a hexagonal hole.
FIG. 3 shows a device according to the invention with three measuring heads.
FIG. 4 is a diagram schematically showing the principle of the present invention.
FIG. 5 is a diagram schematically showing a measuring head adjusting mechanism including a radius adjusting means and an adjusting means for adjusting the height to the rolling center.
[Explanation of symbols]
3 Tubes L1-L4 Laser-ultrasonic-measuring head

Claims (9)

In a non-contact on-line measurement method of the wall thickness of the pipe in a high temperature state for detecting an undesired inner wall structure of a hot rolled pipe to be measured, the pipe is distributed around the pipe. Using a measuring device comprising up to four laser-ultrasonic-measuring heads, a portion of the undesired inner wall structure of the hot-rolled tube is removed during the rolling process or immediately after the rolling process. Scanning is performed by swinging the measuring head in the circumferential direction, and reconstructed by a computer as an undesired inner wall structure of the tube using the symmetry of the polygonal shape inside the wall of the tube cross section. Each measuring head scans a different inner polygonal portion of the tube as an unwanted inner wall structure, and at least one of these measuring heads depends on the inner polygonal shape of the unwanted inner wall structure of the tube. Determined Hot wall thickness measuring method and performing scanning by swinging in the circumferential direction of the tube over an angle portion that. The hot wall pressure measuring method according to claim 1, wherein the rolling process is a stretch reduce process. The hot wall thickness measuring method according to claim 1 or 2, wherein the oscillation cycle of the measuring head is determined depending on a rolling speed. A device for non-contact on-line measurement of the wall thickness of the tube in a hot state for detecting an undesired inner wall structure of a hot rolled tube to be measured, the measuring device being distributed around the tube (3) Are formed from a maximum of four compact laser-ultrasound-measuring heads (L1 to L...), And reflected from the surface of the tube (3) in the measuring head (L1). An optical element is housed together with an excitation / irradiation laser for condensing carrier light including an ultrasonic signal, and the non-circularity of the tube is determined using the symmetry of the polygonal shape inside the wall of the cross section of the tube (3). A control stand (7) including an electronic control and evaluation device (6) for reconfiguration as a desired inner wall structure is combined with the measuring device, and at this time, the measuring heads (L1 to L ...) are shaken. To the undesired inner wall structure of the tube (3) by means of a moving device That is configured to be swung Te circumferentially hot wall thickness measuring device according to claim. The apparatus for measuring a high-temperature wall thickness according to claim 4, wherein an output signal of ultrasonic evaluation corresponding to the wall thickness value is further processed by a computer belonging to the control table.   Three measuring heads (L1 to L3) are evenly distributed around the tube and measured together in order to measure the tube (3) in which the blank tube is manufactured in a tilt rolling process and stretch-reduced. The hot wall thickness measuring device according to claim 4 or 5, wherein the hot wall thickness measuring device can swing by 70 °. Four measuring heads (L1 to L4) are evenly distributed around the pipe in order to measure the tube (3) produced by the inclined rolling process and stretch-reduced, and these measuring heads 6. The hot wall thickness measuring device according to claim 4 , wherein at least one of the first wall and the second wall is swingable by about 70 °. Three or four measuring heads (L1 to L3 or L4) are distributed on the outer circumference of the tube (3) in order to measure the tube (3) rough rolled and stretch reduced in a continuous rolling line. The hot wall thickness measuring device according to any one of claims 4 to 7 , wherein at least one of these measuring heads is swingable by about 90 °.   A plurality of oscillating measuring heads (L1 to L ...) are arranged, and their oscillating angles (ψ) partially overlap each other. The hot wall thickness measuring apparatus as described.

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